Coil component

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-168518, filed on 14 Oct. 2021, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a coil component.

Well known in the art is a coil component in which a coil is provided in an element body made of magnetic material containing metal powder and resin. Patent Document 1 discloses a coil component including a coil having both end portions extracted to end surfaces of the element body, and a pair of external terminals respectively provided on the end surfaces of the element body and electrically connected to the end portions of the coil.

The above-described coil component is required to have Electro-Static Discharge (ESD) resistance that does not cause insulation breakdown even when large static electricity is instantaneously applied. In particular, the ESD resistance against an extremely high transient voltage (for example, 25 kV) is required for an in-vehicle coil component.

The inventors have repeatedly studied the ESD resistance of the coil component, and have newly found a technique capable of improving the withstand voltage against the transient voltage.

According to the present disclosure, a withstand voltage against a transient voltage of a coil is improved.

According to one aspect of the present disclosure, there is provided A coil component including an element body made of a magnetic material including metal powder and resin, the element body having an upper surface and a lower surface parallel to each other, and a pair of end surfaces orthogonal to the upper surface and the lower surface, an insulating substrate disposed in the element body, the insulating substrate extending parallel to the upper surface and the lower surface, and is exposed at each of the pair of end surfaces, and a first coil body disposed in the element body and formed on the upper surface of the insulating substrate, the first coil body including a first planar coil having a first connection end portion, a first lead-out end portion, and a first turn portion connecting the first connection end portion and the first lead-out end portion, and a first insulator covering the first planar coil in the same layer as a layer in which the first planar coil is formed, a second coil body disposed in the element body and formed on the lower surface of the insulating substrate, the second coil body including a second planar coil having a second connection end portion connected to the first connection end portion of the first planar coil via the insulating substrate, a second lead-out end portion, and a second turn portion connecting the second connection end portion and the second lead-out end portion, and a second insulator that covering the second planar coil in the same layer as the layer in which the second planar coil is formed, and a pair of external terminals respectively provided on the end surfaces of the element body and respectively connected to the first lead-out end portion of the first planar coil and the second lead-out end portion of the second planar coil, wherein at least one of the first insulator and the second insulator is formed over the entire width of the end surface on the insulating substrate and is exposed, and an insulating layer interposed between the external terminal and the element body is formed in a remaining region of an exposed region in the end surface.

In the coil component, since the end surface of the element body is divided into the region where the insulating layer is formed or the region where the first insulator or the second insulator is exposed and the element body is not exposed, the external terminal provided on the end surface and the element body are not in direct contact with each other. Therefore, even when a high transient voltage is applied between the pair of external terminals, insulation breakdown is unlikely to occur, and the withstand voltage of the coil component against the transient voltage is improved. In the first insulator and the second insulator, voids are less likely to occur than in the insulating layer, and insulation breakdown is less likely to occur than in the insulating layer. In the above-described coil component, by exposing the entire width of the end surface of the element body, the reliability of the withstand voltage with respect to the transient voltage is improved compared to a case where the insulating layer is formed on the entire area of the end surface.

In a coil component according to another aspect, both the first insulator and the second insulator are formed over the entire width of the end surface on the insulating substrate and are exposed, and the insulating layer is formed in the remaining region of the pair of end surfaces.

In a coil component according to another aspect, wherein the insulating layer covers at least a portion of the first insulator or the second insulator exposed at the end surface.

In a coil component according to another aspect, the first coil body includes a first insulating layer covering the first planar coil from the upper surface side and is exposed at the end surface, and the second coil body includes a second insulating layer covering the second planar coil from the lower surface side and is exposed at the end surface.

Hereinafter, various embodiments and examples will be described with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and redundant description is omitted.

As shown in, the coil componentaccording to the embodiment has a rectangular parallelepiped outer shape. For example, the coil componentmay be designed to have dimensions of long side 1.2 mm, short side 1.0 mm, and height 0.5 mm. Alternatively, as another example, the coil componentmay be designed to have dimensions of long side 2.0 mm, short side 1.2 mm, and height 0.6 mm. As still another example, it may be designed with dimensions of long side 2.5 mm, short side 2.0 mm, and height 1.2 mm.

The coil componentincludes a pair of external terminalsA andB, an element body, and a coil portionembedded in the element body.

The element bodyhas a rectangular parallelepiped outer shape and has six surfacesto. Among the surfacestoof the element body, the upper surfaceand the lower surfaceare parallel to each other, the end surfaceand the end surfaceare parallel to each other, and the side surfaceand the side surfaceare parallel to each other.

The element bodyis made of a magnetic material containing metal magnetic powder and resin (metal magnetic powder-containing resin). The magnetic metal powder-containing resin is a binder powder in which magnetic metal powder is bound by a binder resin. The metal magnetic powder contains, for example, iron example, permalloy, sendust, FeSiCr, FeSi, carbonyl iron, amorphous alloy, nanocrystal, or the like, which contains iron and is an alloy system. The binder resin is, for example, a thermosetting epoxy resin. In the present embodiment, the content of the metallic magnetic powder in the binder powder is 75 to 92 vol % in terms of volume percent, and 95 to 99 wt % in terms of weight percent. From the viewpoint of magnetic properties, the content of the metallic magnetic powder in the binder powder may be 80 to 92 vol % in terms of volume percent and 97 to 99 wt % in terms of weight percent.

The coil portionincludes a first coil body, an insulating substrate, and a second coil body. To be specific, the first coil bodyis provided on the upper surfaceof the insulating substratelocated on the upper surface side of the element body, and the second coil bodyis provided on the lower surfaceof the insulating substratelocated on the lower surface side of the element body. In the present embodiment, the pattern shape of the first coil bodyviewed from the upper surfaceside of the insulating substrateis the same as the pattern shape of the second coil bodyviewed from the lower surfaceside of the insulating substrate.

The insulating substrateis a plate-shaped member extending in parallel to the upper surfaceand the lower surfaceof the element body. As shown in, the insulating substrateincludes an elliptical ring-shaped coil forming portionextending along the long-side direction of the element body, and a pair of frame portionsA andB extending along the short-side direction of the element bodyand sandwiching the coil forming portionfrom both sides. Further, the coil forming portionis provided with a circular through holeat an edge portion of the oval opening. The through holeis filled with a via conductor to electrically connect an inner endof the first planar coiland an inner endof the second planar coil, which will be described later.

As the insulating substrate, a substrate obtained by impregnating a glass cloth with a cyanate resin (BT (bismaleimide triazine) resin: registered trademark) and having a thickness of 60 μm can be used. In addition to the BT resin, polyimide, aramid, or the like can be used. Ceramic or glass can also be used as the material of the insulating substrate. The insulating substratemay be a mass-produced printed circuit board material, or may be a plastic material used for a BT printed circuit board, a FR4 printed circuit board, or a FR5 printed circuit board.

The first coil bodyis provided on the upper surfaceof the substrate in the coil forming portion. As shown in, the first coil bodyincludes a first planar coilconstituting a part of the coilof the coil componentand a first insulator.

The first planar coilis a substantially oval spiral air-core coil wound around the openingof the coil forming portionin the same layer on theof the insulating substrate. The number of turns of the first planar coilmay be one or a plurality of turns. In the present embodiment, the number of turns of the first planar coilis three to four. The first planar coilhas an outer end portion(first extraction end portion), an inner end portion(first connection end portion), and a first turn portionconnecting the outer end portionand the inner end portion. The outer end portionis provided so as to be exposed from the end surfaceof the element bodyand connected to the external terminalA. The inner end portionis provided in a region covering the through holeof the insulating substrateand has a circular shape when viewed from the thickness direction of the insulating substrate. The first planar coilis made of Cu, for example, and can be formed by electrolytic plating.

The first insulatoris provided on the upper surfaceof the insulating substrateand is a thick-film resist patterned by known photolithography. The first insulatordefines a growth region of the first planar coiland covers the first planar coilin the same layer in which the first planar coilis formed. In the present embodiment, the first insulatorincludes an outer-walland an inner-wallthat define the contour of the first planar coil, and a partition wallthat separates an inner turn and an outer turn of the first turn portionof the first planar coil. The first insulatorfurther includes an exposed portion. The exposed portionis a wall-shaped portion exposed to the end surfaceof the element bodyand extends along the end surface. As shown in, the exposed portionextends across the entire width of the end surfaceso as to sandwich the outer end portionof the first planar coil. The first insulatoris made of, for example, epoxy resin.

The first planar coilis formed by plating growth in a growth region defined by the first insulator. The first planar coilincludes a seed patternpatterned on the upper surfaceof the insulating substrateand a plating portiongrown on the seed pattern

As shown in, the first coil bodyfurther includes a protective film(first insulating layer) that integrally covers the first planar coiland the first insulatorfrom the upper surfaceside of the element body. The protective filmis made of, for example, epoxy resin. The protective filmenhances the insulation between the metal magnetic powder contained in the element bodyand the first planar coil.

The second coil bodyis provided on the lower surfaceof the substratein the coil forming portion. As shown in, the second coil bodyincludes a second planar coilconstituting a part of the coilof the coil componentand a second insulator.

The second planar coilis a substantially oval spiral air-core coil wound around the openingof the coil forming portionin the same layer on the lower surfaceof the insulating substrate. The number of turns of the second planar coilmay be one or a plurality of turns. In the present embodiment, the number of turns of the second planar coilis three to four. The second planar coilhas an outer end portion(second extraction end portion), an inner end portion(second connection end portion), and a second turn portionconnecting the outer end portionand the inner end portion. The outer end portionis provided so as to be exposed from the end surfaceof the element bodyand connected to the external terminalB. The inner end portionis provided in a region covering the through holeof the insulating substrateand has a circular shape when viewed from the thickness direction of the insulating substrate. The second planar coilis made of Cu, for example, and can be formed by electrolytic plating.

The second insulatoris provided on the lower surfaceof the insulating substrate, and is a thick-film resist patterned by known photolithography. The second insulatordefines a growth region of the second planar coiland covers the second planar coilin the same layer in which the second planar coilis formed. In the present embodiment, the second insulatorincludes an outer-walland an inner-wallthat define the outline of the second planar coil, and a partition wallthat separates an inner turn and an outer turn of the second turn portionof the second planar coil. The second insulatorfurther includes an exposed portion. The exposed portionis a wall-shaped portion exposed to the end surfaceof the element bodyand extends along the end surface. As shown in, the exposed portionextends over the entire width of the end surfaceso as to sandwich the outer end portionof the second planar coil. The second insulatoris made of, for example, epoxy resin.

Like the first planar coil, the second planar coilis formed by plating growth in a growth region defined by the second insulator. The second planar coilincludes a seed patternpatterned on the lower surfaceof the insulating substrateand a plating portiongrown on the seed pattern

As shown in, the second coil bodyfurther includes a protective film(second insulating layer) that integrally covers the second planar coiland the second insulatorfrom the lower surfaceside of the element body. The protective filmis made of, for example, epoxy resin. The protective filmenhances the insulation between the metal magnetic powder contained in the element bodyand the second planar coil.

The first planar coilprovided on the upper surfaceof the insulating substrateand the second planar coilprovided on the lower surfaceof the insulating substrateare connected to each other at their inner end portionsandvia a via conductor in a through-holepenetrating the insulating substratein the thickness direction. In the present embodiment, the first planar coil, the second planar coil, and the via conductor constitute an air-core coilaround the openingof the insulating substrate. The coilhas coil axes parallel to a thickness direction of the insulating substrate(i.e., a direction in which the upper surfaceand the lower surfaceface each other).

The first planar coiland the second planar coilare wound such that current flows in the same direction (i.e., the same circumferential direction when the insulating substrateis viewed from the thickness direction) when voltage is applied between both ends of the coil(i.e., the outer end portionof the first planar coiland the outer end portionof the second planar coil). In the present embodiment, as shown in, the circumferential direction of the first planar coilfrom the outer end portiontoward the inner end portionis clockwise, and as shown in, the circumferential direction of the second planar coilfrom the inner end portiontoward the outer end portionis clockwise. Since currents flow in the same direction in the first planar coiland the second planar coil, generated magnetic fluxes are superimposed on each other to strengthen each other.

The pair of external terminalsA andB are provided on the end surfacesandof the element body, respectively, and cover the entire regions of the end surfacesand, respectively. In the present embodiment, the external terminalsA andB are formed of resinous electrodes, for example, of resins containing Ag powder. The external terminalsA andB can be formed by metallic plating. The external terminalsA andB may have a single-layer structure or a multi-layer structure.

The pair of external terminalsA andB may be configured such that each of the external terminalsA andB includes a portion covering the upper surface, the lower surfaceand the side surfacesandnear the end surfacesand, and the portion covering the portion continuously extending from the portion covering the end surfaceand. In this case, the insulating layer is also formed in regions of the upper surface, the lower surface, and the side surfacesandin which the external terminalsA andB are formed so as to be interposed between the external terminals and the element body.

Here, insulating layersA andB are formed in the remaining regions of the exposed regions of the first insulatorand the second insulatorin the end surfacesandof the element body. Since the exposed regions of the first insulatorand the second insulatorextend over the entire width of the end surfacesand, each of the insulating layersA andB is divided into two regions that sandwich the exposed region in the vertical direction. The insulating layersA andB can be formed by, for example, forming on the whole surfaces of the end surfacesandof the element bodyand then removing unnecessary portions (exposed regions of the first insulatorand the second insulatorin the present embodiment) by laser irradiation or the like. As shown in, the insulating layersA andB cover part or all of the insulating substrateand the protective filmsandexposed at the end surfacesand, and are in direct contact with the insulating substrateand the protective filmsand. The insulating layersA andB may cover a part of at least one of the outer end portionof the first planar coiland the outer end portionof the second planar coilexposed to the end surfaceand. The insulating layersA andB may be made of resins such as epoxy resins. The thicknesses of the insulating layersA andB are, for example, 10 nm to 100 μm.

The external terminalsA andB are not in direct contact with the metallic magnetic powder-containing resins constituting the element bodyin the exposed regions where the first insulatorand the second insulatorare exposed. In the region other than the exposed region, since the insulating layersA andB are interposed between the external terminalsA andB and the element body, the external terminalsA andB are not in direct contact with the metallic magnetic powder-containing resins constituting the element body.

By adopting a configuration in which the external terminalsA andB are not in direct contact with the metallic magnetic powder-containing resins constituting the element bodyas in the coil componentdescribed above, high ESD resistance can be obtained. That is, even when a high transient voltage (for example, 25 kV) is applied between the pair of external terminalsA andB, insulation breakdown is less likely to occur, and improvement in breakdown voltage with respect to the transient voltage can be realized.

In addition, in the first insulatorand the second insulator, voids (pinholes) are less likely to occur than in the insulating layersA andB, and insulation breakdown is less likely to occur than in the insulating layersA andB. The first insulatorand the second insulatorcan be formed by photolithography, and the rate of occurrence of pinholes in the first insulatorand the second insulatorcan be lower than the rate of occurrence of pinholes in the insulating layersA andB. Therefore, by exposing the first insulatorand the second insulatorover the entire width of the end surfacesandof the element bodyas in the above-described coil component, the reliability of the withstand voltage against the transient voltage is improved compared to the case where the insulating layersA andB are formed over the entire area of the end surfacesand

In addition, since the first insulatorand the second insulatorare exposed over the entire width of the end surfacesandof the element body, it is possible to allow positional deviation when forming the insulating layersA andB to some extent. That is, when the insulating layersA andB are patterned (unnecessary portions are removed) by laser irradiation or the like, since the first insulatorand the second insulatorare exposed over the entire width of the end surfacesandof the element body, direct contact between the external terminalsA andB and the element bodycan be avoided even if a slight positional deviation occurs.

In this case, the insulating layer (e.g., insulating layerB) on the other end surface (e.g., end surface) side can be omitted, and the insulator (e.g., second insulator) exposed on the other end surface (e.g., end surface) does not need to be exposed over the entire width of the end surface. The external terminalsA andB are not in direct contact with the metallic magnetic powder-containing resins constituting the element body.

Although the embodiments of the present disclosure have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present disclosure. For example, the planar shape of the coil is not limited to an elliptical annular shape or a rectangular annular shape, and may be an annular shape or a polygonal annular shape. The exposed shape of the coil end portion is not limited to a circular shape or a rectangular shape, and may be an elliptical shape or a polygonal shape.